1. Field of the Invention
In general, the present invention relates to a collective line-termination apparatus and a line-termination network. More particularly, the present invention relates to reduction of an apparatus cost, reduction of power consumption and improvement of reliability of a collective line-termination apparatus and a line-termination network.
2. Description of the Related Art
With the rapid popularization of the Internet, the use of a line-termination apparatus (DSU) connected between a terminal such as a personal computer installed in an enterprise or at home and a high-speed ISDN transmission line has become the general way of establishing communication through the Internet. By the way, in a construction such as a building and an apartment, a plurality of workers and residents use a plurality of terminals. Thus, if a DSU is installed for each terminal, the cost of the DSU installation will increase. In order to solve this problem, a collective line-termination apparatus is employed. The collective line-termination apparatus accommodates a plurality of interface boards and a power-supply board. The interface boards each serve as an interface between a terminal and a higher-level apparatus. On the other hand, the power-supply board supplies power to the interface boards. Each of the interface boards can be plugged in or pulled out from the collective line-termination apparatus so that, when an interface board is not used, it can be removed.
When the collective line-termination apparatus itself is no longer used, the apparatus is just removed. If a specific interface board is no longer used, only the specific board is removed from the collective line-termination apparatus. If such an interface board is removed or pulled out before a power-supply interruption is reported to an interface board at a higher level, a frame signal representing an abnormal frame and having a deteriorated optical signal level is transmitted to the higher-level interface board. Such a frame signal is detected by the interface board at the higher level as a warning against a state of out-off-synchronization or a deterioration of the signal level. Such an alarm is thus an error caused by the removal or the pulling out of the specific interface board. In order to allow the interface board at the higher level to recognize an error correctly, it is necessary to inform the higher-level interface board of a cause of an error. In this particular case, a power-supply interruption is reported to an interface board at a higher level before the interface board is removed or pulled out to solve the problem. Conventionally, when a collective line-termination apparatus itself is no longer used, a power-supply switch provided on the apparatus is turned off. When the power-supply switch is turned off, a notice of a power-supply interruption is output to an interface board at a higher level by using a backup power supply provided on each of interface boards employed in the collective line-termination apparatus. When a specific interface board is no longer used, a power-supply-interruption alarm switch provided on the interface board or on the case of the collective line-termination apparatus for each interface board is turned on. When the power-supply-interruption alarm switch is turned on, the specific interface board outputs a notice of a pseudo power-supply interruption to the interface board at the higher level. The power-supply interruption is called a pseudo power-supply interruption because the supply of power to the specific interface board is not really interrupted as long as the board remains mounted on the collective line-termination apparatus. Thus, power is supplied by the power-supply board to the specific interface board, keeping the board in an operating state till the board is removed from the apparatus.
The conventional collective line-termination apparatus has the following problems.
1. With an interface board mounted on the collective line-termination apparatus, the power supply of the board is not turned off, keeping the board in an operating state to transmit frames to an interface board at a higher level even if the board is no longer used. Thus, there is raised a problem of wasteful consumption of power.
2. A backup circuit is required for each interface board, increasing the cost.
3. The actual implementation of the collective line-termination apparatus does not leave any space for installing a power-supply-interruption alarm switch for each interface board in the interface boards or on the cabinet of the apparatus. Without such a power-supply-interruption alarm switch, it is impossible to notify an interface at a higher level of a notice of a power-supply interruption from an external source in case a specific interface board employed in the collective line-termination apparatus is no longer used.
4. Recognition of whether or not a notice of a power-supply interruption has been transmitted normally by the collective line-termination apparatus to a higher-level apparatus is not established clearly.
5. In the event of a power-supply interruption of the collective line-termination apparatus, the power-supply board or a backup circuit provided on an interface board drives all circuits mounted on the interface board. Since a backup circuit with a large capacity is required, the size of the backup circuit is also large, becoming a big load mounted on the collective line-termination apparatus.
6. In a terminal, a line-termination apparatus and/or a higher-level apparatus, frames are exchanged between the line-termination apparatus and an interface board at the higher level even if, for example, the power-supply switch of the terminal is turned off. That is to say, there is no interlock mechanism that works in the event of a power-supply interruption, leading to a state in which individual units are operating independently of each other in an uncoordinated manner. As a result, power is consumed wastefully in the system as a whole.
It is thus an object of the present invention to provide a line-termination network and a collective line-termination apparatus allowing power consumption to be reduced.
It is another object of the present invention to provide a collective line-termination apparatus that allows the cost to be reduced.
It is a further object of the present invention to provide a line-termination network and a collective line-termination apparatus which establish clear recognition of a power-interruption notice.
In accordance with an aspect of the present invention, there is provided a collective line-termination apparatus having a power-supply board and a plurality of interface units each serving as an interface between a terminal connected to the interface unit and a higher-level apparatus, the collective line-termination apparatus comprising a power-supply-interruption-notification requesting means provided in each of the interface units and used for outputting a request signal making a request for notification of a power-supply interruption; a first switch provided in each of the interface units and used for passing on or cutting off power generated by the power-supply board; a power-supply-interruption-notification-information insertion means provided in each of the interface units and used for inserting power-supply-interruption-notification information into a first predetermined bit position in a first frame to be transmitted to the higher-level apparatus; a power-supply-interruption-confirmation-information reception means provided in each of the interface units and used for receiving power-supply-interruption-confirmation information inserted into a second predetermined bit position in a second frame to be transmitted by the higher-level apparatus; and an alarm generation means provided in each of the interface units and used for generating an alarm signaling the fact that the associated power-supply-interruption-confirmation-information reception means does not receive the power-supply-interruption-confirmation information even after a period of time with a predetermined length lapses since an issuance of the request signal by the associated power-supply-interruption-notification requesting means to make a request for notification of a power-supply interruption, wherein the first switch is turned off to cut off power generated by the power-supply board when the power-supply-interruption-confirmation-information reception means receives the power-supply-interruption-confirmation information.
In accordance with another aspect of the present invention, there is provided a collective line-termination apparatus having a power-supply board and a plurality of interface units each serving as an interface between a terminal connected to the interface unit and a higher-level apparatus, the collective line-termination apparatus comprising an insertion/removal notification unit provided in each of the interface units, connected to one of the terminals connected to the interface unit and used for outputting information on insertion/removal indicating an insertion or a removal; a first switch provided in each of the interface units and used for passing on or cutting off power generated by the power-supply board; a power-supply-interruption notification means provided in each of the interface units and used for transmitting a first frame including inserted power-supply-interruption information to the higher-level apparatus; and an insertion/removal confirmation means provided in each of the interface units and used for requesting the power-supply-interruption notification means to transmit the first frame to the higher-level apparatus when the insertion/removal notification unit outputs information on insertion/removal indicating a removal, wherein the first switch is controlled to turn on and off in accordance with the information on insertion/removal.
The above and other objects, features and advantages as well as the manner of realizing them will become more apparent and, in addition, the present invention itself will be best understood from a careful study of the following detailed description of some preferred embodiments of the invention and appended claims defining the scope of the invention with reference to accompanying diagrams showing the embodiments.